CVE-2001-1030 in Squid
Summary
by MITRE
Squid before 2.3STABLE5 in HTTP accelerator mode does not enable access control lists (ACLs) when the httpd_accel_host and http_accel_with_proxy off settings are used, which allows attackers to bypass the ACLs and conduct unauthorized activities such as port scanning.
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Analysis
by VulDB Data Team • 09/30/2025
The vulnerability identified as CVE-2001-1030 affects Squid proxy server versions prior to 2.3STABLE5 when operating in HTTP accelerator mode. This security flaw represents a critical configuration oversight that fundamentally undermines the proxy server's access control mechanisms. The vulnerability specifically manifests when administrators configure the proxy with both httpd_accel_host and http_accel_with_proxy off settings, creating a dangerous misconfiguration that renders access control lists ineffective.
The technical flaw stems from the improper handling of access control enforcement within Squid's HTTP accelerator mode. When the httpd_accel_host directive is configured to specify an accelerator host and http_accel_with_proxy is set to off, the proxy server fails to initialize or enforce the standard access control list mechanisms that would normally restrict client access based on predefined rules. This configuration creates a scenario where the proxy operates in a mode that bypasses its fundamental security controls, allowing any connecting client to potentially perform actions that should be restricted by the configured ACLs.
The operational impact of this vulnerability is severe and multifaceted. Attackers can exploit this weakness to bypass access restrictions and conduct unauthorized activities including port scanning, protocol probing, and potentially gaining access to restricted resources within the network. The vulnerability essentially provides a backdoor that allows malicious actors to circumvent the proxy server's security policies, which could lead to unauthorized network access, data exfiltration, or further exploitation of the network infrastructure. This represents a classic privilege escalation scenario where normal access controls are bypassed to gain elevated capabilities.
This vulnerability maps to CWE-284 Access Control Bypass, which specifically addresses situations where the system fails to enforce proper access controls or allows unauthorized access to protected resources. The flaw also aligns with ATT&CK technique T1071.004 Application Layer Protocol: DNS, as it enables attackers to bypass network controls and potentially use the proxy for reconnaissance activities. Organizations using affected Squid versions in HTTP accelerator mode are particularly at risk since the vulnerability exists in the core proxy functionality rather than being a secondary feature.
The recommended mitigation strategy involves upgrading to Squid version 2.3STABLE5 or later, which contains the necessary fixes to properly enforce access control lists even when the specified configuration parameters are used. Administrators should also review their proxy server configurations to ensure that httpd_accel_with_proxy is set appropriately based on their security requirements. Additionally, implementing network segmentation and additional monitoring controls can help detect and prevent exploitation attempts. Organizations should conduct thorough security assessments of their proxy server configurations to identify any instances where this vulnerability may be present, particularly in environments where strict access controls are required for network security compliance.